OK - a better answer than my earlier lazy cut and pasting would be
ONE Example of a Zline would be (but please note, it is
any pa that would encourage a zline to be formed)
Imagine price is basing (just moving in a little a tennis court between a and b {up a bit - down a bit})
This PA would draw certain traders eye to the possibility of price breaking out north or south.
Lets say price breaks out south - these guys SELL
If they are sellers on the breakout, they have their BUY stops all over the place. (to close a sell you buy, whether for a profit or a loss - you buy)
Price moves down over the next few hours (or mins)
Some of these traders do not take profit where they
should*
Price inevitably turns north - the further north price travels the more panicky the short breakout traders get. ( they think " I should have got out" maybe it will turn south again - here - here or here"
The closer price gets to their entry - Their trading psychology is such that they all move their BUY stops into the same place - the original breakout, or a handy pointy place near enough to draw their eye to put their BUY stop.
Now the market has engineered a scenario where thousands of traders are willing to
BUY IN THE EXACT SAME PLACE where they should be
selling - so the pro's SELL into those BUYS (importantly, the market don't move much as there may be enough buyers to fulfil the sellers needs - so the seller get the best price, rather than each order pushing the market lower to find willing buyers)
Price returns to the breakout - at the original breakout, traders bail out with their BUY stops (or is that bye

) to the pros who want to sell
* So where should they have taken their profit - from the guys who made there own Zline to trade north -
try to get into their skins to feel their anxiety
Or, to put it simply
As
Aliassmith posted so eloquently
"A zero line is a line or area where traders give back their profits
From their current trade."
"MOJO 1)Self-confidence, Self-assuredness. As in basis for belief in ones self in a situation. Esp/In context of contest or display of skill such as going into battle. 2)Ability to bounce back from a debilitating trauma and negative attitude YEH BABY